本地數據存儲之UserDefaults

 

UserDefaults支持的基本數據類型包含：

NSData, NSString, NSNumber, NSDate, NSArray, or NSDictionary

 

對於自定義的類，如果直接存儲會出現如下錯誤：

Property list invalid for format (property lists cannot contain objects of type ‘CFType’)

 

如果想存儲自定義的類，需要對其進行編碼即轉換為基本數據類型。

 

類定義，以及轉換為NSDictionary類型：

 

@interface XYZToDoItem : NSObject

@property NSString *itemName;
@property BOOL completed;
//@property (readonly) NSDate *creationDate;
@property NSDate *creationDate;

- (NSDictionary *) encodedItem;

@end

 

 

@implementation XYZToDoItem

#pragma Used for encoded objects to be able to save to UserDeafaults
- (NSDictionary *) encodedItem
{
    return [NSDictionary dictionaryWithObjectsAndKeys:self.itemName, @itemName,
            [NSNumber numberWithBool:self.completed], @completed,
            self.creationDate , @creationDate, nil];
}

@end

 

 

調用的地方，存儲如UserDefault裡，並且讀取轉換為相應的類：

- (void) saveUserDefaultsOwn
{
    XYZToDoItem *item1 = [[XYZToDoItem alloc] init];
    item1.itemName = @Buy milk;
    //[self.toDoItems addObject:item1];
    XYZToDoItem *item2 = [[XYZToDoItem alloc] init];
    item2.itemName = @Buy eggs;
    //[self.toDoItems addObject:item2];
    XYZToDoItem *item3 = [[XYZToDoItem alloc] init];
    item3.itemName = @Read a book;
    //[self.toDoItems addObject:item3];
    
    
    NSUserDefaults *userdefaults = [NSUserDefaults standardUserDefaults];
    [userdefaults setObject:[item1 encodedItem] forKey:@item1];
    [userdefaults setObject:[item2 encodedItem] forKey:@item2];
    [userdefaults setObject:[item3 encodedItem]forKey:@item3];
    
    [userdefaults synchronize];
}

- (void) readUserDeafultsOwn
{
    NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
    NSDictionary *dic1 = [[NSDictionary alloc] init];
    
    
    dic1 = [userDefaults objectForKey:@item1];
    
    XYZToDoItem *item1 = [[XYZToDoItem alloc] init];
    item1.itemName = [dic1 objectForKey:@itemName];
    item1.completed = [dic1 objectForKey:@completed];
    item1.creationDate = [dic1 objectForKey:@creationDate]; //initial it is readonly, not right

    dic1 = [userDefaults objectForKey:@item2];
    XYZToDoItem *item2 = [[XYZToDoItem alloc] init];
    item2.itemName = [dic1 objectForKey:@itemName];
    item2.completed = [dic1 objectForKey:@completed];
    item2.creationDate = [dic1 objectForKey:@creationDate]; //initial it is readonly, not right
    
    dic1 = [userDefaults objectForKey:@item2];
    XYZToDoItem *item3 = [[XYZToDoItem alloc] init];
    item3.itemName = [dic1 objectForKey:@itemName];
    item3.completed = [dic1 objectForKey:@completed];
    item3.creationDate = [dic1 objectForKey:@creationDate]; //initial it is readonly, not right
    
    //XYZToDoItem *item2 = [userDefaults objectForKey:@item2];
    //XYZToDoItem *item3 = [userDefaults objectForKey:@item3];
    
    [self.toDoItems addObject:item1];
    [self.toDoItems addObject:item2];
    [self.toDoItems addObject:item3];
}

綜上為簡單的對復雜的類進行簡單封裝並且讀取的例子。